Linear actuators are commonly used to propel or oscillate mechanical components such as components that are used in aerospace applications. Actuators used in the aerospace industry, including linear actuators, are commonly made of many interworking parts. When one of the interworking parts breaks or becomes damaged, it may be necessary to replace the entire actuator. Similarly, each actuator in its entirety may need to be custom designed for each application. The assembly costs for such actuators is controlled through the selection of raw materials as well as incremental simplification of part geometries to facilitate manufacture.
In non-aerospace applications, actuators can be made of larger connected parts or components that, when in operation, cause free play between (or relative movement of) adjacent components. In these non-aerospace applications this type of free play is not typically detrimental to the function of the actuators. Non-aerospace actuators therefore have not needed a mechanism for compensating for free play.
Conventional designs of actuators for aerospace applications use threaded or otherwise pre-loaded mechanical connections between the numerous interworking parts and are not modular. These parts and the components on which the actuators operate are therefore not subject to free play. As such, there has not been a need for a mechanism in aerospace actuators to compensate for free play.
Actuators used in non-aerospace applications typically use a snubbing arrangement that includes a plunger entering into a cavity to establish an annular orifice at a predetermined distance from the end of the stroke. This narrowing, annular orifice acts to progressively restrict the fluid discharged from the unpressurized chamber until the end of the stroke is reached. The size of the annulus is chosen to provide the desired reduction in piston velocity.
Snubbing schemes used in non-aerospace actuators depend upon the resistance to fluid through passages. This can be problematic because the resistance in the fluid is sensitive to many factors. To ensure that the snubbing action is consistent, the rod and cylinder assemblies that comprise the actuator must be carefully aligned by controlling the manufacturing tolerances on mating features to a very high degree of precision, driving up cost. Nevertheless, the amount of resistance to the fluid flow is highly dependent on the area of the annulus formed by the plunger, the shape of the annulus (it may be irregular due to positional misalignment), and the change in fluid viscosity due to temperature changes.
Snubbing schemes for actuators used in aerospace applications commonly require holes to be drilled in the cylinder of the actuator in areas of high stress concentration creating a fatigue issue especially in applications requiring high pressure (5000 psi, for example). FIG. 11 illustrates a prior art blanked passage snubbing arrangement. There is unrestricted flow until the piston ring crosses the first drilling at which point the only fluid path is through the restrictor. The size of the effective orifices in the restrictor is chosen to provide the desired reduced piston velocity. Drilling a hole close to the junction of the cylinder body and head can lead to failures in high pressure applications. Other designs can require an overlap of the lug end over the outer cylinder that would require fluid to pass through two separate components that require complex and costly sealing arrangements.
The present invention addresses at least one of the above problems.